Effects of surface treatment for sapphire substrate on gallium nitride films

Abstract High quality GaN films with low dislocation density have been successfully grown on the c -plane sapphire substrate, which the sapphire is etched by molted KOH solution. The solid-phase epitaxy starts from the regions with no etched pits where there are some micro-sidesteps to help to nucleate and then spreads laterally by increasing V/III ratio to form continuous GaN films. The crystal quality of epilayer is improved with the lengthening of etching time, but when the etching time is prolonged to some extent, the size of etching pit is too large to coalesce of two wings, the epilayer crystal quality is decreased, so the etching time for sapphire substrate has crucial effect on the epilayer crystal quality. The full widths at half maximum of the X-ray diffraction curves for the GaN films grown on the sapphire substrate, which has been etched for 50 min, in (0 0 0 2) plane and ( 1 0 1 ¯ 2 ) plane are as low as 202.68 arcsec and 300.24 arcsec, respectively, and the etch-pit density (EPD) of those etched in molten KOH is reduced down to 3.1 × 10 5  cm −2 . The epilayer exhibits atomically smooth surface, whose root mean square roughness is found to be 0.184 nm. Compared with the conventional epitaxial lateral overgrown technique. The technique is much simpler, the voids and crystallographic tilt can also be overcome.